Thymocytes and RelB‐dependent medullary epithelial cells provide growth‐promoting and organization signals, respectively, to thymic medullary stromal cells

Abstract

The thymic medulla is composed of distinct epithelial cell subsets, defined in this report by the reactivity of two novel antibodies, 95 and 29, raised against mouse thymic epithelial cell lines. These antibodies were used to probe the development of medulla in wild-type or mutant thymuses. In CD3 epsilon-deficient mice where thymocyte maturation is arrested at the CD4- CD8- stage, few scattered 95+ and 29+ epithelial cells are found. When few mature thymocytes develop as in CD3- zeta/eta mice, expansion and organization of 95+ but not 29+ cells, becomes detectable. In RelB-deficient mice, T cell maturation proceeds normally but negative selection is inefficient due to the lack of thymic medulla and dendritic cells. Strikingly, 29+ epithelial cells are absent and 95+ medullary epithelial cells are scattered throughout the thymus, intermingling with CDR1+ cortical epithelium. In chimeric mice lacking only dendritic cells, the corticomedullary junction persists and both 95+ and 29+ epithelial cells are localized in the medulla. These results suggest that two types of signals are required for development of thymic medulla. A growth signal depends upon the presence of maturing thymocytes, but organization of the thymic medulla requires the presence of activated 29+ medullary epithelial cells.

Normal Thymic Architecture and Negative Selection Are Associated with Aire Expression, the Gene Defective in the Autoimmune-Polyendocrinopathy-Candidiasis-Ectodermal Dystrophy (APECED)

“…45). Moreover, thymic epithelial subpopulations with a cortical and medullary phenotype can be distinguished at this point in time (36). Abundant Aire expression was demonstrated at E16, a time during thymic development when the formation of DP thymocytes has been initiated but TCR-mediated thymic selection has not yet begun.…”

“…Thymocytes were obtained by tissue disruption using frosted glass slides, whereas TEC were prepared by enzymatic digestion of whole thymi as described elsewhere (36,37). After enrichment of low-density cells by Percoll gradient for the sorting of TEC, cell subsets were stained with a combination of CD3, CD4, CD8, CD11c, and CD45 (all from PharMingen, San Diego, CA), as well as mAbs 29 (36), G8.8 (38), and CDR1 (39), respectively.…”

“…After enrichment of low-density cells by Percoll gradient for the sorting of TEC, cell subsets were stained with a combination of CD3, CD4, CD8, CD11c, and CD45 (all from PharMingen, San Diego, CA), as well as mAbs 29 (36), G8.8 (38), and CDR1 (39), respectively. The different lymphocyte and stromal subpopulations were sorted by flow cytometry (FACStar; Becton Dickinson, Mountain View, CA) to a purity of at least 98%.…”

“…Several surface markers have been described that are expressed on medullary epithelial cells (36,39,(47)(48)(49)(50). The Ab designated 29 recognizes a subpopulation of TEC thought to represent stromal cells bearing features of "activated" cells (36,51).…”

“…The Ab designated 29 recognizes a subpopulation of TEC thought to represent stromal cells bearing features of "activated" cells (36,51). cells, stromal cells were isolated by gentle digestion of thymic fragments.…”